The present invention relates to a bolometer, i.e. a device for measuring the energy of electromagnetic radiation in certain wave length regions by utilizing the change in resistance of a thin conductor caused by the heating effect of the radiation. The change in resistance is then measured by a Wheatstone bridge.
Devices of this type are already known and, in actual practice, usually utilize two bolometer strips which are as similar as possible and which are inserted into adjacent branches of the bridge circuit. Only one of these strips is exposed to the radiation so that an independence with reference to the ambient temperature is obtained. In a known bolometer the bolometer strip is constructed in form of a meandering conductor strip of gold or nickel which is supported on an insulating layer of magnesium oxide. The insulating layer is in turn arranged on an absorber layer of gold. It has been found that this strip construction is extremely sensitive to mechanical stresses because of the danger that the insulating layer may break. Moreover, it is difficult to manufacture such a strip because the insulating layer has a tendency to develop holes during the manufacture and this then results in shorting of the strip which thereby becomes unusable. Overall, the median life expectancy of a bolometer utilizing such a strip is therefore relatively short.
Another bolometer type is described in a publication of the Batell-Institute e.V., Frankfurt, Federal Republic of Germany, No. 479/0.5. In this construction the bolometer strip consists of a meander-shaped conductor of gold which is supported on a free insulating layer of aluminum oxide and has a radiation absorbing material coated over it. This construction has been found to have the disadvantage that the aluminum oxide layer--which is produced by anodizing--is brittle and therefore also cannot withstand mechanical stresses.